So this one has a lot of variables in it, I could really use some help here. I recently returned my truck back to stock after running a 408 stroker for about a decade (it was a glass cannon). I was able to get ahold of my original 360 motor, it had been left outside with the intake manifold off, gotten rained on and such but was in surprisingly good shape when I took it apart to rebuild it.

Because gaskets are only about $250 and taking the block to be machine and rebuilding it would cost me probably around $1200 minimum I decided to give it a shot without rebuilding the bottom end, just cleaning it as well as I could without removing the crank or pistons.

I replaced the oil pump, cleaned and inspected everything as well as I could, replaced the timing chain and sprockets and coated everything in moly assembly lube. When I switched out the original 360 engine to the 408 stroker ten years ago it was smoking pretty badly I had to pour a lot of oil in it to keep it running which I did for years out of necessity.

I did find that I got the Pcv valve and breather valve hoses flip flopped, and went ahead and replaced them and corrected the issue which improved how the truck runs and lessened the smoke issue but it’s still there.

I also got a mt2500 snap on scanner on ebay and used it to do the fuel synch, it strangley will read 4 degrees if I go counter clockwise on the distributor but if I go clockwise to zero it just stays at reading 0 degrees on the fuel synch even though it should be showing me negative numbers.

As far as the smoke is concerned it’s a bit unique, the engine sounds and runs great when you fire it up, and doesn’t smoke at all when idling or in neutral. However when you have it in gear and are either decelerating or accelerating you can see the oil pressure spiking up and then once it’s high enough it will start smoking blue smoke like crazy out the exhaust pipe.

If you kick it into neutral any time the pressure spikes and drive it gently you can get it to stop smoking and have normal oil pressure. If you put your foot into it and let the pressure build it’ll start smoking so badly that eventually it starts backfiring like a gunshot. When it has its first cold start of the day it runs rougher and builds up the pressure much faster until it warms up.

I’ve put about 200 miles on it, both out of necessity because it’s my only vehicle right now and also because I’m trying to see if I can get the rings to seat. It hasn’t had any issues with overheating except for maybe the first ten miles or so it ran a bit hot, presumably while these old rings were getting unstuck.

I just did the first oil and oil filter change on this motor and it seemed to perk up a lot and run much better and have less troubles with high oil pressure after I did it. I still am test driving it some more after fixing the pvc valve issue which improved the engine sound and smoke a lot but you can definitely still put your foot into it and make it smoke and backfire if you try to.

I can rebuild this engine if I really have to, but I’d like to avoid it if it’s possible and make it work as is if there is a way. At the very least I want to properly diagnose what went wrong with it before I do the rebuild. The main reason I don’t think this is an issue with the oil ports being clogged is that it really doesn’t seem to have any issues with overheating and also seems to run super well when you don’t ask too much of it and kick it into neutral soemtimes when the oil pressure spikes.

This one is a real noodle scratcher guys, please help me figure out good solutions or diagnostics. I’m quite experienced with this truck and engine now, but this one seems to be a stumper. I’d rather not give up and tear it down for a proper rebuild if I can help it. I’m considering sea foam in the crankcase to flush it or some such, but I’m reticent to go that route as sea foam is unlikely to actually solve an issue like this.

Feel free to ask me for more details or pictures and such, I’ll make sure to check this forum at least a couple times a week and try to keep up with my responses.

 

If it was smoking when you took it out, sat outside for 10 years, open to the elements, and you essentially just dropped it back in, why are you surprised that it still smokes?

That said, you have a couple problems there. Blowby is likely one of 'em, and a questionable pressure regulator on the oil pump. Don't know if it got some dirt in there that found it's way to the pan, or if it was just crap right out of the box.....

 

If you didn't actually remove the pistons, what rings are there to seat? they've been seated for 200k miles or more it sounds like, compression test?

you can buy these trucks left and right with no frame left under em, no body left around em or no trans left behind em for 500 bucks, i found two just today in my area. The motors probably run better than what you got. get a better engine and 200 bucks worth of rust to haul in for scrap

 

The head scratcher is why you didn't take apart the bottom end? At least put new rings in and hone the cylinders. And you didn't say what psi oil you have(mechanical gauge not the one in the truck).

 

I didn’t buy new rings and bearings and hone the engine because of time and budget constraints, and because the engine had about 150k on it and was running when I pulled it. It smoked but it had a blown plenum pan gasket that leaked oil on the exhaust valves for a few years while I was driving it around and pouring oil in it (I was 19 and had never even heard of the plenum pan gasket) and it dropped one exhaust valve seat and chipped that one valve. I went through and replaced all the exhaust valves and lapped them all till the seats were good and it passed the Prussian blue test.

I think realistically (speaking from experience here) the bottom end rebuild adds about $1200 to my costs minimum. It only cost me $200 in engine gaskets to give it a shot without rebuilding the bottom of end and to me it was very much the right move, I needed the truck running in time for the return to office since I’m a federal worker and they threw that at us remote workers.

It actually runs pretty well as far as it doesn’t overheat and it gets me a to b and if I don’t put my foot into it and shift early it doesn’t smoke too badly. It has no troubles with overheating, I’ve put a good 200 miles on this engine now.

Honestly I’d love to hear some more constructive questions and ideas, I don’t have space to buy an entire second truck and use it for parts, nor do I care too. What I would like to do is some more diagnostics and Hail Mary passes on this current engine to learn what is wrong with it so I can rebuild it properly and not have this issue post rebuild.

In about a month I should be done with my Honda cb450 engine rebuild and then I’ll have that as a daily driver and I can start tearing down the truck for a proper complete rebuild if we can’t solve this smoking issue without a full rebuild. Until then I’m asking for ideas on the current situation, not what I should do if I had infinite time and money.

 

I am suspecting the oil pressure valve too, it shouldn’t be too hard to get too since I can pull the oil pan without doing too much to the truck. I just would be surprised if it’s the piston rings because the engine only has about 150k miles on it. I’ve read consistently that when you leave a block to sit for a long time the rings get stuck and it can take up to 1000 miles to clear off the cylinder walls and get them to stop smoking.

I think the high oil pressure is a big clue for sure, I just am not aware of anything besides blow by or a oil pressure valve that could cause this. Maybe plugged up oil ports but then wouldn’t I have issues with overheating? The fact it runs so cool makes me suspect it’s not clogged ports.

 

I would be tempted to just pick up a donor engine, and rebuild that, then just swap when the time comes. That way, if the weather is crappy, you don't *have* to ride the bike.

In the meantime, a leakdown test would tell you the internal condition of rings/valves..... and how soon you are going to need that replacement. If it runs good otherwise, might just be trashed rings.... which WILL make it burn oil. (and foul plugs fairly quickly.) If you don't have the capability to do a leakdown test, do a compression test. See what the numbers look like.

Part of your oil pressure problems may just be the sensor itself. Not like they aren't known to be somewhat less than accurate......

 

I do have a compression tester and leakdown tester I was thinking in that direction myself. Has anyone here heard of this after an engine has been sitting for a while the rings get stuck or some such and you have to drive it to reseat them and clear off the cylinder walls or some such? My dad swears he's seen old derelict v8s come back to life (in his days as a performance mechanic in the 70s) just by driving the p!ss out of them.

I actually have been considering replacing the oil pressure sending unit just to see if it improves because it does like to bounce around a lot like when they are busted and it is located in a spot where no matter how careful I am it's easy to damage when doing an engine swap. Is there a way to see it's busted for sure using my Snap on MT2500 scanner? Also does anyone understand why the scanner wouldn't be showing any negative numbers when I do the fuel synch and run the distributor backwards? It only shows like 4 degrees when I scoot it counter clockwise and then just goes to zero degrees once I go at all back to clockwise, it won't show negative degrees even if I run it so far clockwise the engine is about to die. I have the correct cartridges, main and troubleshooter, and the correct k13 personality key for it, and a fresh high voltage 9v battery in it. As it is I had to do it by ear/feel because everything past zero is just more zero I can't fine tune it with the scanner as it is right now.

 

I love the donor engine idea, but how do I get one that is functional without breaking the bank? I reckon I'd just be rolling the dice again right? Plus if that engine works I would no longer need my current engine, and it will take a lot of space up in my yard or shed. Luckily I live in Sacramento and I tend to enjoy the cold and have decent enough gear so weather isn't much of an issue typically.

 

I think I got all my motors off craigs list, Before that it was the news paper/Tradin times classifieds(telling my age here). You can scout the junk yards too.